Method and apparatus for manufacturing paint rollers

ABSTRACT

A method of manufacturing paint rollers includes the steps of extruding a cylindrical plastic core through a rotating extruder head, and securing an absorbent sheet material onto an outer surface of the core in a continuous process.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation in part of U.S. patent applicationSer. No. 09/024,971, filed Feb. 6, 1998 now U.S. Pat. No. 6,159,320,which is hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to a continuous process for fabricating a paintroller having an extruded plastic core and a hellically-wound absorbentfabric bound to the exterior surface of the core.

BACKGROUND OF THE INVENTION

Paint rollers are and have been commonly used to apply paints and othercoating materials to surfaces for many years. Paint rollers have aunique set of required specifications due to the physical nature of theapplication process and due to the wide range of paints and othercoating materials that the roller may be exposed to in routine use.Paint rollers must have a rigid inner core that is manufactured in acylindrical shape with a high level of precision so that when the paintroller rotates relative to the surface to be painted, it coats evenly.The cylindrical shape of the roller should not yield, bend or deformunder significant stress even when the outer fabric has absorbed paintover an extended period. Even slight deformation of the roller shape maycause uneven paint application.

A manufacturer of paint rollers must assume that the roller could beexposed to any of a wide range of fluid compositions. Some paints arewater-based and others are oil or solvent-based. Many differentpigments, solubilizing agents, surfactants, viscosifiers, emulsifiers,etc., are used in paints, stains and other surface coating compositions.Ideally, the roller core should be inert or at least resistant to allsuch ingredients so that its rigid cylindrical shape is maintained evenafter long periods of use, washing and reuse. A sturdy solvent-resistantcore yields a longer effective life-time for the roller which is animportant objective for those who buy and use paint rollers.

Paint rollers typically have an absorbent fabric material fixed to theexternal surface of the core. The fabric should be uniformly absorbentand bonded to the core in a manner which remains in tact when the rolleris exposed to paint. The fabric must also be applied and bonded to thecore in a precise and continuous configuration so that there is nooverlap or gaps in the fabric which could result in a non-uniform paintapplication pattern.

Various procedures have been used by others to produce paint rollersthat satisfy to some extent the specifications discussed above. However,a significant disadvantage with prior manufacturing processes is thatthey require multiple on and off-line procedures. For example, adesirable core material due to its water and solvent resistivity isextruded plastic such as polyethylene or polypropylene. Typically thecore material is extruded, formed and cooled in one process, then putthrough at least a second process where the core is wrapped with fabric.Multiple on and off-line processing sequences add to manufacturing costsand manual work requirements. Thus, there is a need for a paint rollermanufacturing method in which a high quality, solvent-resistant paintroller can be fabricated in a single continuous on-line process.

SUMMARY OF THE INVENTION

The invention provides a method, system and apparatus for manufacturingpaint rollers through the use of an extruder employing a rotating headso that a plastic core can be extruded and rotated simultaneously whileother process steps including application of an outer absorbent materialare performed downstream in a single continuous process. The result is areduction in manufacturing cost compared to prior methods, and a highquality paint roller product, in particular, a solid rigid core that ishighly durable and resistant to water and solvents.

In a preferred embodiment of the invention, a cylindrical polypropylenecore is extruded. The rotating core then translates through a vacuumsizing and cooling chamber. Next, the core passes through a winding andpulling station which is coordinated with the drive unit of theextruder. The core is subsequently plasma-treated prior to extruding anepoxy adhesive layer on the external surface of the core. Finally, thecore is heated, wrapped with fabric and cut into discrete paint rollers.All of the steps are performed in a continuous time- andlocation-coordinated procedure with minimal if any manual involvement.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic flow chart illustrating a paint roller fabricationmethod in accordance with a preferred embodiment of the invention.

FIG. 2 is a perspective view of an extruder employed in the presentinvention to produce a cylindrical core for a paint roller.

FIG. 3 is a sectional view of the output end of an extruder employing arotatable head in accordance with a preferred embodiment of the presentinvention.

FIG. 4 is a perspective view of a vacuum sizing and cooling chamber usedin the present invention.

FIG. 5 is a side view of a plasma discharge unit used in the presentinvention.

FIG. 6 is a side view of an extrusion assembly used to apply epoxy in apreferred process embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a system and process for producing paint rollersin a continuous process including extrusion of a highly solventresistant core and bonding of an absorbent fabric material downstream.The continuous processing feature of the invention allows significantreduction in manufacturing costs and improvement in overall efficiencyand product quality compared to prior processes.

FIG. 1 is a schematic diagram illustrating process steps in a preferredembodiment of the invention. The first step 20 involves extrusion of aplastic cylindrical pipe or core 21. Extruder 22 receives plastic resin,preferably polypropylene, through hopper 24. The plastic resin melts andis extruded through rotating head 26 into a hollow cylindrical form,core 21, that rotates around axis 28, while translating forward at aconstant velocity, under control of drive unit 29. The size of extruder22 is based on the plastic resin used and the desired output in poundsper hour of plastic core 21. In a preferred embodiment of the invention,a 3½ inch 24:1 L/D air-cooled Meritt Extruder from Meritt DavisCorporation, as shown in FIG. 2, is used along with a rotating extruderhead, as shown in FIG. 3, from Guill Tool & Engineering Company of RhodeIsland.

Further details of extruder 22 and head 26 are illustrated in FIGS. 2and 3. FIG. 2 shows extruder 22 including hopper 24 at one end forreceiving raw materials such as polypropylene pellets or particles forsubsequent melting and extrusion through rotating head 26, as shown inFIG. 3, which is attached to output end 30 of extruder 22. FIG. 3 is adrawing of rotating head assembly 26 including die 31 that defines theouter diameter of extruded core 21, and tip 32 that defines the innerdiameter of extruded core 21. The gap between die 31 and tip 32 definesthe thickness of core 21. Sprocket or gear 33 facilitates rotation ofdie 31 and tip 32 around rotational axis 28. Seals 34 prevent meltedmaterial from reaching bearings 35 that are used to permit smoothrotational movement of die 31 and tip 32 relative to the outer housing.In the present invention, die 31 and tip 32 rotate at approximatelybetween 100-140 rpms.

Rotating head 26 is powered by SCR drive motors in drive unit 29 todrive both die 31 and tip 32 of head 26 to allow for the extrusion to berotated in an exact relationship to the forward movement of theextruding core. Controls are used to maintain a plus/minus ratio of0.01-percent between extruder 22 and head 26. This allows for maximumcontrol of the helical angle at which the core rotates in relation tothe forward motion of the core to assure a uniform seam at the fabricapplication station downstream. Preferably, core 21 moves 3.375 inchesof lineal forward movement per 360 degrees of rotation of the core. Thisis required to accommodate the 2.875 inch slit width fabric used tocover the core downstream. The motors that control the rotation of head26 are adjustable for fine tuning to assure proper butting of the seamin the fabric application step of the process.

In the second step 37 of the process shown in FIG. 1, plastic core 21enters a vacuum sizing and cooling tank 38 where a vacuum is applied tothe exterior of core 21 along with chilled water spray that cools core21 down to a “Freeze Point” of about 225° F. This is the point at whichfull stability is achieved in the plastic. The dimensions are set with atolerance of +/−0.005 inch to the outside and inside diameters.Typically the inside diameter of the paint roller is 1.485 inches. Thewall thickness is 0.045 inch with larger walls as required by theprofessional market.

FIG. 4 shows a perspective view of vacuum sizing and cooling tank 38.Vacuum sizing and cooling tank 38 can be procured from ExtrusionServices, Inc. of Akron, Ohio. Tank 38 employs a stainless steel tunnelor chamber 39 through which the core translates after extrusion.Polypropylene core 21 is approximately 500° F. when it exits head 26 ofextruder 22. By the time the core reaches entry end 39 a of chamber 39,core 21 has cooled to approximately 400-450° F. Water jets or sprayinside chamber 39 continue to cool core 21 so that by the time it exitsoutput end 39 b of chamber 39, core 21 is approximately 200-225° F.

In the third step 40, as illustrated in FIG. 1, core 21, after travelingapproximately 2-3 feet from output end 39 b of chamber 39, enters guide42 made of a hollow steel mandrel that has an inside diameter of 0.010inches larger than the outside diameter of plastic core 21. The lengthof guide 42 is about 30 inches. The end of guide 42 is located withinapproximately 2 inches from the leading edge of winding belt 44. Belt 44is configured to pull and continue rotation of plastic core 21. Windingbelt 44 is controlled by drive unit 29 of extruder 22 so that windingbelt 44 precisely maintains the rotation rate and translational velocityof core 21 to match the rate at which core 21 is exiting and rotatingfrom extruder 22. After core 21 exits winding belt 44, it enters asecond hollow steel guide 46 of the same diameters as first guide 42.This allows core 21 to be properly aligned and positioned for the nextstep. Coordination of the rotational drive functions of extruder head 26and winding belt 44 on opposite sides of cooling chamber 38 is animportant feature of the invention because it allows core 21 to berotated, in sync with fabric wrapping downstream, without deformation ofthe core's cylindrical shape even when core 21 is somewhat fluid as itexits extruder 22.

In the fourth step 50 of the process illustrated in FIG. 1, the externalsurface of core 21 is treated with high voltage electrical plasma inorder to attract and accommodate adhesive applied in the next step ofthe process. In a preferred embodiment a surface treater obtained fromIntercon Industries Corporation of Wisconsin is used. The surfacetreater employs a corona discharge head including two electrodes thatgenerate an air blown electrical arc to form a treatment plasma. Thecorona discharge electrodes are positioned approximately ¼ inch awayfrom the external surface of rotating core 21. The plasma treatmentincreases the surface energy and tension on the outer surface of plasticcore 21 which allows easier application and improved adhesion of epoxyin the next step. As shown in FIG. 5, surface treater 52 employs coronadischarge head 53 which includes electrodes 54 and 56. Electrode 54generates a plasma treatment area 57 that is elliptical in shape on theexternal surface of core 21 as it rotates and translates past surfacetreater 52. Similarly, electrode 56 generates a plasma treatment pattern58 on the external surface of core 21 adjacent plasma treatment pattern57. Other numbers of heads, electrodes and combinations of treatmentpatterns can be used. The important thing is that, given the rates offorward movement and rotation of core 21, the overall treatment shouldtotally cover the external surface of core 21.

Between plasma treatment step 50 and the next step 60, as shown in FIG.1, core 21 should have at least about 3-4 seconds to react beforeapplication of epoxy in step 60. A thin layer of epoxy is applied to thesurface in step 60. This is accomplished by use of gear pumps for boththe “a” and “b” resins, driven by an SCR-type motor which extrudes athin film of epoxy onto the surface of plastic core 21. Adhesive resinswhich work well for this application are sold under the trademarksMASTER 5200A and 5200B, and MASTER GRIP 5200A and 5300B, which areavailable from Fielco Industries of Huntingdon Valley, Pa.

FIG. 6 illustrates an epoxy extrusion unit for dispensing a thin layerof epoxy resin, parts A and B, on the external surface of core 21. Across-section of core 21 is seen in FIG. 6 with its axis of rotationperpendicular to the page. Core 21 is held against V-block 22, in part,by the fabric wrapping unit downstream. A doctor blade or knife bar 23is positioned near the external surface of core 21 for the purpose ofmetering the thickness of the adhesive layer being applied to core 21.The thickness of the extruder adhesive layer is preferably approximately3-5 thousandths of an inch. Subparts of the adhesive are combined andmixed in dispenser 24 prior to dispensing the adhesive through tip 25near the edge of doctor blade 23.

Once the film is applied, it is heated to 300° F. by use of a parabolicinfrared heater in step 70. This allows the epoxy film to rapidly set sothe continuous core can be cut in a short amount of time.

Fabric is introduced in step 80 at the proper helical angle to match theangle of core rotation originally established by extruder 22 androtating head 26 at the beginning of the process, and as perpetuated bywinding belt 44 in the third step 40 of the process. The fabric isguided onto the core by use of a fabric stand and tensioning device. Thetension on the fabric is preferably about 5-7 pounds to assure that thefabric is embedded into the epoxy film. Core 21 travels approximately 30feet after fabric winding step 80 to accommodate completion of epoxycuring.

Finally, in step 90 fabric-covered core 21 enters traveling cut-off saw92 which is programmed to cut the core into pre-selected lengths. Thecut cores are discharged onto an accumulation table. The core lengthsare then ready to be processed into finished lengths and packaged.

An experiment was performed to measure how much the core shrinks as itcools after exiting the extruder head. In accordance with the methodsdescribed above, the outer diameter of the core as it left the extruderhead was 2.010-inches. The core translated from the extruder head to thecooling chamber without any internal chuck or support structure. Whenthe core entered the cooling chamber approximately 4-inches downstreamfrom the extruder head, the outer diameter of the core was approximately1.690-inches. Upon exiting the cooling chamber, 16-inches furtherdownstream, the outer diameter was 1.595-inches. The temperaturetransition over this distance was approximately 470° F. to 90° F. Thesignificant amount of contraction which occurred as the core cooleddemonstrates the importance of enabling extrusion of a rotating coreinto free space, without any internal chuck, support structure, or anyother type of molding device.

Although the invention has been disclosed in its preferred forms, thespecific embodiments thereof as disclosed and illustrated herein are notto be considered in a limiting sense, because numerous variations arepossible. Applicants regard the subject matter of their invention toinclude all novel and non-obvious combinations and subcombinations ofthe various elements, features, functions, and/or properties disclosedherein.

We claim:
 1. A method of manufacturing paint rollers in an inlineprocess comprising extruding a rotating hollow cylindrical plastic corethrough a rotating extruder head wherein the core exits the extruderhead without an internal support structure inside the core, moving thecore through a cooling chamber, winding and pulling the core downstreamfrom the moving step, and wrapping and securing an absorbent sheetmaterial onto an outer surface of the core downstream from the windingand pulling step.
 2. The method of 1 wherein a rotational angle of thecore is defined by the rate of rotation of the extruder head and theforward movement of the core, the securing step including the step ofintroducing a fabric to the outer surface of the core at a helical anglematching the rotational angle of the core so that a uniform seam betweensuccessive wraps of fabric is achieved.
 3. The method of claim 1 furthercomprising the step of cooling the core between the extruding step andthe securing step.
 4. The method of claim 3 wherein the cooling stepincludes the step of spraying water on the core.
 5. The method of claim1 further comprising the step of vacuum sizing the core after it exitsthe extrusion head before the core cools to a freeze point.
 6. Themethod of claim 5 wherein the vacuum sizing includes the step of movingthe core into a vacuum sizing chamber and applying a vacuum to the outersurface of the core.
 7. The method of claim 1 further comprising thestep of vacuum sizing the core in the cooling chamber between theextruding step and the securing step.
 8. The method of claim 1, whereinthe winding and pulling steps are performed by a winding belt.
 9. Themethod of claim 8 further comprising the step of coordinating the rateof extruder rotation and winding belt speed.
 10. The method of claim 8further comprising the steps of moving the core through a first hollowguide mandrel upstream from the winding belt and moving the core througha second hollow guide mandrel downstream from the winding belt.
 11. Themethod of claim 1 wherein the extruding step and the securing step areperformed in a single continuous process.
 12. The method of claim 1further comprising the step of cutting the core into sections accordingto desired paint roller dimensions after the securing step.
 13. Themethod of claim 1 further comprising supporting the core externallydownstream from the cooling chamber.
 14. The method of claim 1 furthercomprising supporting the core externally before and after the windingand pulling step.
 15. The method of claim 1 further comprisingsupporting and guiding the core by hollow guide mandrels upstream anddownstream from the winding and pulling step.
 16. The method of claim 1further comprising applying adhesive to the core before the wrappingstep.
 17. An apparatus for producing paint rollers inline comprising anextruder including a rotatable head configured to extrude a rotatinghollow cylindrical plastic core without an internal support structureinside the core as it exits the head, an extruder drive unit for drivingrotation of the head, a cooling chamber downstream from the extruder, awinder-puller belt downstream from the extruder for controlling rotationand translation of the core, and a fabric application mechanism locateddownstream from the winder-puller belt including a supply of paintroller fabric material.
 18. The apparatus of claim 17 further comprisinga first hollow guide mandrel upstream from the winder-puller belt, and asecond hollow guide mandrel downstream from the winder-puller belt. 19.The apparatus of claim 17 further comprising an epoxy resin extruder forapplying thin films of resin onto an outer surface of the core upstreamfrom the fabric application mechanism.
 20. The apparatus of claim 19further comprising a parabolic infrared heater located downstream fromthe epoxy resin extruder for heating films of epoxy resin prior toapplying fabric.
 21. The apparatus of claim 17 further comprising acut-off saw located downstream from the fabric application mechanism forcutting the core into sections according to desired paint rollerdimensions.
 22. The apparatus of claim 17, wherein the extruder and thefabric application mechanism are operatively connected in a continuouspaint roller fabrication process.
 23. A method of manufacturing paintrollers in an inline process comprising extruding a cylindrical plasticcore through a rotating extruder head without an internal supportstructure inside the core as the core exits the extruder head, movingthe core through a cooling chamber, winding and pulling the core by awinding belt while coordinating the rate of extruder head rotation andwinding belt speed, and securing an absorbent sheet material onto anouter surface of the core downstream from the winding belt.
 24. Anapparatus for producing paint rollers inline comprising an extruderincluding a rotatable head configured to extrude a hollow cylindricalplastic core without an internal support structure inside the core asthe core exits the head, an extruder drive unit for driving rotation ofthe head, a cooling chamber downstream from the extruder, awinder-puller belt for coordinating rotation and forward movement of thecore, the belt being positioned downstream from the extruder andupstream from the fabric application mechanism, wherein thewinder-puller belt is controlled by the extruder drive unit, a firsthollow guide mandrel upstream from the winder-puller belt, and a secondhollow guide mandrel downstream from the winder-puller belt, and afabric application mechanism located downstream from the extruderincluding a supply of paint roller fabric material.
 25. An apparatus forproducing paint rollers inline comprising an extruder including arotatable head configured to extrude a rotating hollow cylindricalplastic core, an extruder drive unit for driving rotation of the head, acooling chamber for cooling the core downstream from the extruder, afabric application mechanism located downstream from the extruderincluding a supply of paint roller fabric material, a winder-puller beltfor coordinating rotation and forward movement of the core, the beltbeing positioned downstream from the extruder and upstream from thefabric application mechanism, wherein the winder-puller is controlled bythe extruder drive unit, and a first hollow guide mandrel upstream fromthe winder-puller belt, and a second hollow guide mandrel downstreamfrom the winder-puller belt.